Drum including annular grid structure

ABSTRACT

A drum comprising an annular grid structure which includes end portions formed only from coils of waved strip material and an intermediate portion formed from alternate coils of waved and planar strip material. The head plates at the ends of the drum have stiffening spokes or ribs connected thereto in a manner accommodating differential expansion and contraction of the head plates and spokes generally radially of the grid structure.

Jan. 1, 1974 United States Patent 1 1 Luthi 7/1966 Bryand 5/1969Spencer....4............... 7/1969 MacKendrick..... 2/1971 Bryand 7/1971Bryand.......................

Primary Examiner-Alfred R. Guest Attorney-David W. Tibbott et al.

[22] Filed: Sept. 15, 1972 Appl. No.: 289,663

[57] ABSTRACT A drum comprising an annular grid structure which includesend portions formed only from coils of waved strip material and anintermediate portion formed from alternate coils of waved and planarstrip material. The head plates at the ends of the drum have 2 4 mm m 1E2 1 9 .N 8 n 6 Ia un 2 m w w m "Hu "W02 1. u .r "Ha NS L hf C S U.mF HN 555 [56] References Cited stiffening spokes or ribs connected theretoin a man- UNITED STATES PATENTS ner accommodating differential expansionand contraction of the head plates and spokes generally radially of thegrid structure.

29/121 R r 29/121 A 22 Claims, 7 Drawing Figures SHEET 1 0F 2 PATENTEDJAN 1 9 4 DRUM INCLUDING ANNULAR GRID STRUCTURE The present inventionrelates to annular honeycomb or grid structures such as, by way ofspecific example, the annular honeycomb drums employed by the pulp andpaper making industry.

Drums of this general type are normally well suited for employment inthe drying of paper webs due to their large percentage ofcircumferential open area and structural rigidity. ln drying apparatusincluding such a drum, the paper web may be driven circumferentiallyaround the grid structure beneath an overlying backing felt while airsupplied at highly elevated temperature (for example, 700 to 900Fahrenheit) is blown outwardly from the drum interior through the gridstructure and the thereupon paper web and backing felt.

ln apparatus of this construction, one or more cooling showers areprovided for automatically directing cooling liquid (for example, liquidat around 60 Fahrenheit) onto the grid structure in the event ofbreakage of the paper web, thereby preventing the scorching of thebacking felt which would otherwise occur upon the engagement of the feltwith the grid structure after such breakage. Hence, in such apparatusupon breakage of the paper web, the grid structure is suddenly cooledfrom around 700 Fahrenheit by the cooling liquid, it being understoodthat a rapid cooling of the grid structure from 700 Fahrenheit to 60Fahrenheit would cause a V2 inch reduction in an 84 inch diameter gridstructure. Notwithstanding this cooling of the grid structure, however,the drum head plates remain at full operating temperature for a periodof time, thereby causing distortion of the grid structure and resultingin such severe bending and yielding adjacent the juncture or the headplates and grid structure as will eventually result in premature drumfailure. Moreover, after the cooling of the grid structure, although thedrum head plates remain hot, the stiffening spokes extending along thehead plates cool to provide a further source of distortion and prematurefailure.

In drying apparatus including a drum ofthe beforedescribed type, thepaper web alternatively may be driven around the grid structure beneathan overlying driven wire while air supplied at the beforementionedhighly elevated temperature is blown inwardly through the wire, web andgrid structure and thence discharged into the interior of the drum at agreatly reduced temperature (for example, around 200 Fahrenheit). lnthis arrangement, upon breakage of the paper web, the grid structurewill be suddenly exposed to air at a temperature much higher than 200Fahrenheit, thereby causing problems similar to those arising upon thebeforedescribed rapid cooling of the grid structure.

An object of the present invention is to provide a new and improved drumincluding annular grid structure, which drum is particularly constructedand arranged to withstand temperature fluctuations of even severalhundred degrees without undue distortion, yielding or failure.

Another object of the invention is to provide a new and improved drumincluding annular grid structure, which drum is particularly constructedand arranged to accommodate differential expansion and contraction ofits component parts.

Another object is to provide a new and improved drum including annulargrid structure, which drum is particularly constructed and arranged topermit relative expansion and contraction of the head plates andtherewith associated stiffening spokes or ribs.

Another object is to provide a drum including a new and improved annulargrid structure.

Other objects and advantages of the invention will be apparent from thefollowing description taken in connection with the accompanying drawingswherein, as will be understood, the preferred embodiment of theinvention has been given by way of illustration only.

In accordance with the ivnention a drum may comprise an annular gridstructure including juxtaposed, laterally interconnected strip means,such strip means for at least one portion of the grid structurecomprising only waved strip means and such strip means for anotherportion of the grid structure comprising both waved and planar stripmeans, also, in accordance with the invention, a drum may comprise headplate means adjacent at least one end of the grid structure, stiffeningmeans extending along such head plate means, and means interconnectingthe head plate means and stiffening means permitting relative movementthereof to accommodate differential expansion and contraction of thehead plate means and stiffening means.

Referring to the drawings:

FIG. 1 is a view schematically illustrating a drum constructed inaccordance with one embodiment of the invention;

FIG. 2 is an enlarged, fragmentary perspective view of the drum shown inFIG. 1;

FIG. 3 is a further enlarged, fragmentary, elevational view showing oneof the end portions of the grid structure of the drum;

FIG. 4 is an enlarged elevational view showing one of the drum headplates and the therewith associated stiffening spokes;

. FIG. 5 is an enlarged, fragmentary, sectional view taken on line 5-5of FIG. 4, looking in the direction of the arrows;

FIG. 6 is an enlarged, fragmentary, sectional view taken on line 66 ofHO. 5, looking in the direction of the arrows; and

FIG. 7 is an enlarged, fragmentary, sectional view taken on line 77 ofFIG. 5, looking in the direction of the arrows.

Referring more particularly to the drawings wherein similar referencecharacters designate corresponding parts throughout the several views,the illustrated drum comprises an annular, cylindrical, honeycomb orgrid structure 10 which includes circumferential end portions, eachdesignated generally as 12, and a circumferential intermediate portion14 between and unitary with the end portions 12. The relative lengths ofthe end portions 12 and intermediate portion 14 axially of the gridstructure 10 are, of course, variable in different embodiments of thegrid structure 10. However, it will be understood that the length ofeach end portion 12 is preferably only a relatively small portion of theoverall length of the grid structure 10. For example, in a gridstructure 10 approximately nine feet in length each end portion 12 mightbe of around six inch length with the intermediate portion 14 formingthe remaining approximately eight foot length of the grid structure 10.

The end portions 12 are of identical construction and each comprise onlysheet metal, waved or non-planar strip material 16 helically wound tolongitudinally extend circumferentially of the grid structure 10 withjuxtaposed coils of the waved strip material 16 directly laterallyinterconnected. The waved strip material 16 is arranged with itsgreatest transverse or widthwise dimension at least generally radiallyof the grid structure and the juxtaposed interconnected coils of thewave strip material 16 cooperate to therebetween define openings 18 atleast generally radially through the thickness of the grid structure 10.The waved strip material 16, per se, may be of any suitable waved ornonplanar configuration and advantageously, as illustrated, is of theconstruction described in United States Patent Application Ser. No.289333, entitled GRID STRUC- TURE AND STRIP MEANS THEREFOR which wasfiled by John P. Rich on the same date as the present application and isassigned to the assignee of the present invention. More particularly, asillustrated, the waved strip material 16 includes alternating generallydiagonal segments 20 and connecting segments 22, the diagonal segments20 extending across the central plane of the waved strip material 16 andadjacent ones of the connecting segments 22 being on opposite sides ofsuch central plane. The connecting segments 22 are formed of arcuate,generally sharp or pointed configuration and each cooperate with thediagonal segments 20 on opposite sides thereof to define a generally V-shaped portion of the waved strip material 16. The connecting segments22 hence bound the at least generally pointed apexes of such generallyV-shaped portions and are each provided with one or more enlargedsections 24 at which juxtaposed coils of the waved strip material 16 areinterconnected, such as by welding.

The intermediate portion 14 of the grid structure 10 includes both thebeforedescribed waved strip material 16 and also sheet metal planarstrip material 26. The waved and planar strip materials 16,26 arehelically wound to longitudinally extend conferentially of the gridstructure 10 in alternate arrangement throughout the length of theintermediate portion 14 and rigidly interconnected (for example, bywelding) at the enlarged portions 24 ofthe connecting segments 22 of thewaved strip material 16. The alternately arranged strip materials 16,26are disposed with their greatest transverse or widthwise dimensions atleast generally radially of the grid structure 10 and cooperate totherebetween define additional openings 18 at least generally radiallythrough the thickness of the grid structure 10. Hence, the intermediateportion 14 throughout its length includes alternate coils of the stripmaterials l6,26,juxtaposed ones of which coils are rigidly laterallyinterconnected at intervals; and, as will be understood, the end coilsof the intermediate portion 14 are each similarly rigidly connected atintervals to the juxtaposed end coil of the thereadjacent end portion12.

As illustrated, the ends of the grid structure 10 are each supported bya supporting means, designated generally as 28, which includes agenerally radially extending wall 32 to which the end coil 30 of therespective, adjacent end portion 12 is affixed, preferably by welding,at the enlarged portions 24. Each supporting means 28, moreover,includes a supporting ring or annular plate 34, unitary with wall 32,which has an outer diameter generally the same as that of the gridstructure l0.

Each end ofthe drum includes an annular head plate 36 which may, asillustrated, close the corresponding end of the grid structure 10. Eachhead plate 36 is along its outer circumference affixed to the supportingring 34 of the thereadjacent supporting means 28, and

along its inner circumference rigidly connected to a hub or hubstructure, designated generally as 38, which comprises a plurality ofannular hub elements 40, 42, 44, and 46. Each annular hub element 44 iswelded or otherwise directly affixed to the inner circumference of thecorresponding head plate 36 and rigidly carries an annular hub element42, projecting internally of the drum coaxial with the grid structure 10which rigidly carries a hub element 46. Each hub element 44, moreover,is affixed to a hub element 40, such as by a plurality of bolts 48, thehub element 40, in turn, being provided with generally radial ribs 40aand carrying a stub shaft 50 adapted to rotatably mount thecorresponding end of the drum.

A plurality of stiffening spokes or ribs 52 are arranged to extend alongeach of the head plates 36 internally of the drum for providing thenecessary stiffness to the head plates 36. More particularly, as shownin FIGS. 4 and 5, the spokes 52 are each arranged to longitudinallyextend generally radially of the grid structure l0 and drum head plate36 and have inner ends 54 generally centrally thereof affixed, such asby welding, to the hub elements 42, 44, 46 whereby the inner end 54 ofeach spoke 52 is rigidly interconnected through a hub structure 38 tothe inner end of the corresponding head plate 36. The outer ends 56 ofthe spokes 52 are generally adjacent the inner circumference of the gridstructure 10, but sufficiently inwardly spaced from the thereadjacentsupporting means 28 to permit longitudinal expansion of the spokes 52generally radially of the grid structure 10. The outer ends 56 of thespokes 52, moreover, each carry a connecting bracket 58 which onopposite sides of the spoke 52 includes openings 60 aligned withcorresponding openings 62,64 through a boss 66 affixed to the head plate36 and the head plate 36, respectively. The openings 60, as shown inFIGS. 5 and 6, are each constructed of substantially larger diameterthan the aligned openings 62,64; and mounting bolts 68 are insertedthrough the aligned sets of the openings 60, 62, 64 to connect the outerends of the spokes 52 to the head plates 36. The portions 70 of thebolts 68 received in the openings 60 are of substantially smallerdiameter than the openings 60, thereby permitting limited relativemovement of the head plates 36 and the spokes 52 generally radially ofthe grid structure 10 to accommodate differential expansion andcontraction of the head plates 36 and spokes 52 generally radially ofthe grid structure 10.

Spaced intermediate its inner and outer ends 54,56, each spoke 52rigidly carries a connecting plate 72, such connecting plate 72 andcooperative connecting elements 74 serving to insure that the spoke 52properly extends along the head plate 36 while permitting differentialexpansion and contraction of the head plate 36 and spoke 52 generallyradially of the grid structure 10. Intermediate the connections of thespokes 52 to the head plates 36-by the connecting plates 72 andconnecting elements 74 and the ends 54,56 of the spokes 52, the spokes52, are, however, not fixedly connected to the head plates 36. Also, tofacilitate relative movement of the spokes 52 and head plates 36generally radially of the grid structure 10 upon their differentialexpansion and contraction, a suitable lubricant is interposedintermediate each connected boss 66 and connecting bracket 58.

From the preceeding description, it will be seen that the inventionprovides new and improved means for accomplishing all ofthezbeforestatedzobjects and advantages. For example, it will be seenthatthe described arrangement and interconnectionof the spokes '52andhead plates 36 enables differential-expansion.and contraction thereofgenerally radially of thegrid structure 10, thereby avoiding;thedistortion, bendingand'yielding problems which would be inherent werethe spokes 52 merely rigidly connected to the head plates 36. Also, itwill be seen that the end portions 12 of the grid structure 10,comprising onlywavedstrip material 16, are extremely strongin3transmitting shear load circumferentially of the grid structure and,as the endsof the grid structure 10 are'held round by the supportingmeans 28 and head plates 36, ovate or egg-shaped de- .flection of theends of the grid structure 10 is prevented; the bendingmoment on thegrid structure 10 is, of course, inherently rather small at its ends.

I! will be understood, however, that, although only a single embodimentof the inventionhas been illustrated and hereinbefore specificallydescribed, the invention is not limited merely to this singleembodiment, but rather contemplates other embodiments and variationswithin the scope of the following claims.

Having thus described my invention, I claim:

1. A drum comprising an annular grid structure including juxtaposed,laterally interconnected strip means, said strip means for at least oneportion of said grid structure comprising only waved strip means, andsaid strip means for another portion of said grid structure comprisingboth waved and planar strip means.

2. A drum according to claim 1, wherein said grid structure includes aplurality of said portions comprising only waved strip means, saidplurality of such portions being separated by a therebetween saidportion comprising both waved and planar strip means.

3. A drum according to claim 1, wherein said strip means longitudinallyextend circumferentially of said grid structure and said one portion ofsaid grid structure is an end portion thereof.

4. A drum according to claim 3, wherein both end portions of said gridstructure comprise only said waved strip means.

5. A drum according to claim 1, further comprising head plate meansadjacent at least one of the ends of said grid structure, stiffeningmeans extending along said head plate means for stiffening said headplate means, and means interconnecting said head plate means and saidstiffening means permitting relative movement thereof to accommodatedifferenting expansion and contraction of said head plate means and saidstiffening means.

6. A drum according to claim 5, wherein said stiffening means comprisesspoke means extending generally radially of said grid structure.

7. A drum according to claim 5, wherein said interconnecting meanscomprises an opening associated with one of said head plate means andstiffening means, and a retainer having a portion in said opening, saidretainer portion being of substantially smaller crosssection than saidopening.

8. A drum according to claim 1, wherein said waved and planar stripmeans longitudinally extend circumferentially of said grid structure,said grid structure includes end portions at opposite ends thereofcomprising only laterally interconnected coils of said waved stripmeans, and said grid structure includes an intermediate portion betweensaid end portions comprising and waved strip means.

9. A drum according to claim 8, further comprising head plate meansadjacent at least one of the ends of said grid structure, a plurality ofspokes extending generally radially of said grid structure along saidhead plate means for stiffening said head plate means, and meansinterconnecting said head plate means and said spokes permittingrelative movement thereof generally radially of said grid structure toaccommodate differential expansion and contraction of said head platemeans and said spokes generally radially of said grid structure.

10. A drum according to claim 9, wherein said means interconnecting saidhead plate means and said spokes comprises an opening associated withone thereof and a retainer having a portion in said opening, saidretainer portion being of substantially smaller crosssection than saidopening.

11. A drum according to claim 9, wherein said spokes have inner endsgenerally centrally of said grid structure and outer ends adjacent theinner circumference of said grid structure, said outer ends of saidspokes are spaced from thereadjacent structure to permit expansion ofsaid spokes generally radially of said grid structure, and saidinterconnecting means connects said spokes adjacent their outer ends tosaid head plate means.

12. A drum according to claim 11, further comprising means rigidlyinterconnecting said inner ends of said spokes with said head platemeans, and connecting means connecting said spokes with said head platemeans at locations spaced longitudinally of said spokes intermediatetheir ends, such connecting means permitting relative movement of saidspokes and said head means generally radially of said grid structure.

13. A drum according to claim 11, comprising said head means, spokes andinterconnecting means at both of its ends.

14. A drum comprising an annular grid structure including interconnectedstrip means, head plate means extending transversely of said gridstructure adjacent one end thereof, a plurality of spokes extendinggenerally radially of said grid structure along said head plate meansfor stiffening said head plate means, and means interconnecting saidspokes and said head plate means permitting relative movement thereofgenerally radially of said grid structure for accommodating differentialexpansion and contraction of said head plate means and said spokes insaid generally radial direction.

15. A drum according to claim 14, wherein said interconnecting meanscomprises an opening associated with one of said head plate means andsaid spokes, and a retainer having a portion in said opening, saidretainer portion being of substantially smaller crosssection than saidopening.

16. A drum according to claim 14, wherein said spokes have inner endsgenerally centrally of said grid structure and outer ends adjacent theinner circumference of said grid structure, said outer ends of saidspokes are spaced from thereadjacent structure to permit expansion ofsaid spokes generally radially of said grid structure, and saidinterconnecting means connects said spokes adjacent their outer ends tosaid head plate means.

17. A drum according to claim 16, comprising means rigidlyinterconnecting said inner ends of said spokes with said head platemeans, and connecting means connecting said spokes with said head platemeans at locations spaced longitudinally of said spokes intermediatetheir ends, and connecting means permitting relative movement of saidspokes and said head plate means generally radially of said gridstructure, the portions of the lengths of said spokes intermediate theirsaid connections to said head plate means being free of fixed connectionto said head plate means.

18. A drum according to claim 17, further comprising lubricant means forfacilitating said relative movement of said spokes and said head platemeans.

19. A drum according to claim 14, wherein said strip meanslongitudinally extends circumferentially of said drum, and furthercomprising second head plate means extending transversely of said gridstructure adjacent the other thereof, a plurality of second spokesextending generally radially of said grid structure, along said secondhead plate means for stiffening said second head plate means, and secondmeans interconnecting said second spokes and said second head platemeans permitting relative movement thereofgenerally radially of saidgrid structure for accommodating differential expansion and contractionof said second head plate means and said second spokes in said generallyradial direction.

20. A drum according to claim 19, wherein said each of said spokes andsaid second spokes has an inner end generally centrally of said gridstructure and an outer end adjacent the inner circumference of said gridstructure, such outer ends of the spokes are spaced from thereadjacentstructure to permit expansion of the spokes generally radially of saidgrid structure, and the spokes are connected adjacent their outer endsby the respective interconnecting means to their respective adjacent oneof said head plate means.

21. A drum according to claim 20, further comprising hub means rigidlyinterconnecting said inner ends of each of the spokes with therespective adjacent one of said head plate means, and connecting meansconnecting each of the spokes with such head plate means at locationsspaced longitudinally of said spokes intermediate their ends, saidconnecting means permitting relative movement of the connected spokesand head plate means generally radially of said grid structure.

22. A drum according to claim 21, wherein each spoke is connectedadjacent its outer end to the respective adjacent one of said head platemeans by an opening associated with one of said head plate means andsaid spokes, and a retainer having a portion in said opening, saidretainer portion being substantially smaller in cross-section than saidopening.

l =l= l

1. A drum comprising an annular grid structure including juxtaposed,laterally interconnected strip means, said strip means for at least oneportion of said grid structure comprising only waved strip means, andsaid strip means for another portion of said grid structure comprisingboth waved and planar strip means.
 2. A drum according to claim 1,wherein said grid structure includes a plurality of said portionscomprising only waved strip means, said plurality of such portions beingseparated by a therebetween said portion comprising both waved andplanar strip means.
 3. A drum according to claim 1, wherein said stripmeans longitudinally extend circumferentially of said grid structure andsaid one portion of said grid structure is an end portion thereof.
 4. Adrum according to claim 3, wherein both end portions of said gridstructure comprise only said waved strip means.
 5. A drum according toclaim 1, further comprising head plate means adjacent at least one ofthe ends of said grid structure, stiffening means extending along saidhead plate means for stiffening said head plate means, and meansinterconnecting said head plate means and said stiffening meanspermitting relative movement thereof to accommodate differentingexpansion and contraction of said head plate means and said stiffeningmeans.
 6. A drum according to claim 5, wherein said stiffening meanscomprises spoke means extending generally radially of said gridstructure.
 7. A drum according to claim 5, wherein said interconnectingmeans comprises an opening associated with one of said head plate meansand stiffening means, and a retainer having a portion in said opening,said retainer portion being of substantially smaller cross-section thansaid opening.
 8. A drum according to claim 1, wherein said waved andplanar strip means longitudinally extend circumferentially of said gridstructure, said grid structure includes end portions at opposite endsthereof comprising only laterally interconnected coils of said wavedstrip means, and said grid structure includes an intermediate portionbetween said end portions comprising laterally interconnected, alternatecoils of said planar and waved strip means.
 9. A drum according to claim8, further comprising head plate means adjacent at least one of the endsof said grid structure, a plurality of spokes extending generallyradially of said grid structure along said head plate means forstiffening said head plate means, and means interconnecting said headplate means and said spokes permitting relative movement thereofgenerally radially of said grid structure to accommodate differentialexpansion and contraction of said head plate means and said spokesgenerally radially of said grid structure.
 10. A drum according to claim9, wherein said means interconnecting said head plate means and saidspokes comprises an opening associated with one thereof and a retainerhaving a portion in said opening, said retainer portion being ofsubstantially smaller cross-section than said opening.
 11. A drumaccording to claim 9, wherein said spokes have inner ends generallycentrally of said grid structure and outer ends adjacent the innercircumference of said grid structure, said outer ends of said spokes arespaced from thereadjacent structure to permit expansion of said spokesgenerally radially of said grid structure, and said interconnectingmeans connects said spokes adjacent their outer ends to said head platemeans.
 12. A drum according to claim 11, further comprising meansrigidly interconnecting said inner ends of said spokes with said headplate means, and connecting means connecting said spokes with said headplate means at locations spaced longitudinally of said spoKesintermediate their ends, such connecting means permitting relativemovement of said spokes and said head means generally radially of saidgrid structure.
 13. A drum according to claim 11, comprising said headmeans, spokes and interconnecting means at both of its ends.
 14. A drumcomprising an annular grid structure including interconnected stripmeans, head plate means extending transversely of said grid structureadjacent one end thereof, a plurality of spokes extending generallyradially of said grid structure along said head plate means forstiffening said head plate means, and means interconnecting said spokesand said head plate means permitting relative movement thereof generallyradially of said grid structure for accommodating differential expansionand contraction of said head plate means and said spokes in saidgenerally radial direction.
 15. A drum according to claim 14, whereinsaid interconnecting means comprises an opening associated with one ofsaid head plate means and said spokes, and a retainer having a portionin said opening, said retainer portion being of substantially smallercross-section than said opening.
 16. A drum according to claim 14,wherein said spokes have inner ends generally centrally of said gridstructure and outer ends adjacent the inner circumference of said gridstructure, said outer ends of said spokes are spaced from thereadjacentstructure to permit expansion of said spokes generally radially of saidgrid structure, and said interconnecting means connects said spokesadjacent their outer ends to said head plate means.
 17. A drum accordingto claim 16, comprising means rigidly interconnecting said inner ends ofsaid spokes with said head plate means, and connecting means connectingsaid spokes with said head plate means at locations spacedlongitudinally of said spokes intermediate their ends, and connectingmeans permitting relative movement of said spokes and said head platemeans generally radially of said grid structure, the portions of thelengths of said spokes intermediate their said connections to said headplate means being free of fixed connection to said head plate means. 18.A drum according to claim 17, further comprising lubricant means forfacilitating said relative movement of said spokes and said head platemeans.
 19. A drum according to claim 14, wherein said strip meanslongitudinally extends circumferentially of said drum, and furthercomprising second head plate means extending transversely of said gridstructure adjacent the other thereof, a plurality of second spokesextending generally radially of said grid structure, along said secondhead plate means for stiffening said second head plate means, and secondmeans interconnecting said second spokes and said second head platemeans permitting relative movement thereof generally radially of saidgrid structure for accommodating differential expansion and contractionof said second head plate means and said second spokes in said generallyradial direction.
 20. A drum according to claim 19, wherein said each ofsaid spokes and said second spokes has an inner end generally centrallyof said grid structure and an outer end adjacent the inner circumferenceof said grid structure, such outer ends of the spokes are spaced fromthereadjacent structure to permit expansion of the spokes generallyradially of said grid structure, and the spokes are connected adjacenttheir outer ends by the respective interconnecting means to theirrespective adjacent one of said head plate means.
 21. A drum accordingto claim 20, further comprising hub means rigidly interconnecting saidinner ends of each of the spokes with the respective adjacent one ofsaid head plate means, and connecting means connecting each of thespokes with such head plate means at locations spaced longitudinally ofsaid spokes intermediate their ends, said connecting means permittingrelative movement of the connected spokes and head plate means generallyradially of said grid structure.
 22. A drum according to claim 21,wherein each spoke is connected adjacent its outer end to the respectiveadjacent one of said head plate means by an opening associated with oneof said head plate means and said spokes, and a retainer having aportion in said opening, said retainer portion being substantiallysmaller in cross-section than said opening.